Phytase is an enzyme that sequentially removes phosphates from the phytate molecule. Phytate (myo-inositol hexakisphosphate) is the principal storage form of phosphorus in many plant tissues such as bran and seeds.
Phosphorus is an essential and limiting nutrient for growth and development of plants. To increase crop yield, large amount of phosphorus fertilizers are applied to cropland each year. However, only 10-20% of the fertilizer is utilized (Holford, 1997, Aust J Soil Res 35: 227-23). The rest of the phosphorus becomes fixed in form and is poorly available to plants (Vance et al., 2003, New Phytol 157: 423-447). The increased soil phosphorous level eventually leads to contamination to water. As phosphorous is a limiting nutrient for aquatic plants as well, an increased water phosphorous level result in eutrophication and decreased water quality. Thus, the large input of phosphorus fertilizer is not only expensive but also nonsustainable.
Phosphorus is an essential dietary requirement for growth and development of animals. Bran and seeds, rich in phytate, constitute major components of animal feeds. However, non-ruminant animals utilize phytate poorly due to the absence of gastrointestinal tract phytase. As a result, non-utilized phytate is excreted by the animals. To cope with the problems, swine and poultry rations are routinely supplemented with inorganic phosphorous or phytase. However, neither approach is satisfactory. In the former, the supplement increases feed costs and increases the phosphorous content in animal waste; in the latter, phytase is expensive and unstable. Animal waste or manure has long been applied as fertilizer to pastures and croplands. Because of phosphorous content in the waste, this practice increases soil phosphorous levels and, eventually, leads to eutrophication.
In the United States, the swine and poultry industries annually generate over 20 million tons of manure containing over 300,000 tons of waste phosphorous (Cromwell et al., Altech Conference Proceedings, 1991). As phosphorus recycles among plants, animals, soil and water, organic phosphorus could make up 20-80% of the total phosphorus in soil and phytate accounts for up to half of the soil organic phosphorus (Dalal, 1977, Adv Agron 29: 83-117). The resulting high soil phosphorus levels pose a server environmental threat.
Thus, there are needs for new, cheap, absorbable phosphorus sources for animals and plants, and needs for means to deal with eutrophication and related environment problems.